This invention relates to a valve for connecting a user port with a pressure port or a return port, including a slidable piston acted upon by a pressure in opposition to the force of a spring, and adapted to shift a closure member from a first into a second valve position, the closure member interrupting the connection between the return port and the user port in the first valve position, and the connection between the pressure port and the user port in the second valve position.
From the German published patent application DOS No. 2,364,413, an accumulator charging valve is known which includes a valve pressurizing or depressurizing the control chamber of a by-pass valve dependent upon the pressure prevailing in an accumulator.
This by-pass valve includes a piston which is slidable by the accumulator pressure acting thereon against the force of a plate spring. The piston has a tappet extending through a return port opening into a valve chamber. Opposite the return port, a pressure port likewise opens into the valve chamber. Furthermore, a user port opens into the valve chamber at right angles to the pressure and return ports. The orifices of pressure and return port at the valve chamber are designed as valve seats adapted to be closed by a ball forming a closure member, with the ball being disposed in the valve chamber with clearance.
In the first valve position, in which the accumulator pressure is below the change-point pressure of the valve, the tappet extends through the return port only to such an extent that it does not project into the valve chamber. By virtue of the pressure prevailing at the pressure port and acting on the ball, the ball is urged upon the valve seat of the return port, thereby closing the latter. The user port is then in communication with the pressure port via the valve chamber.
When the accumulator pressure reaches the change-point pressure of the valve, the force acting on the piston overcomes the force of the plate spring acting in opposition thereto. This causes displacement of the piston until its tappet comes to rest against the ball. For the piston to be displaced still further, it is necessary for the accumulator pressure to continue to increase in order to overcome, in addition to the spring force, also the force with which the ball is urged onto the valve seat of the return port. Only after this additional counterforce has been overcome will the piston be displaced further, with the tappet resting against the ball lifting the ball off the valve seat of the return port and shifting it into the second valve position in which the ball rests upon the valve seat of the pressure port, thereby closing the latter. This provides for communication of the user port with the return port.
By a change in the pressure at the pressure port during the valve position change process it may happen that the spring force and the force of the pressure fluid acting on the ball, which originates from the pressure port, are in equilibrium with the force of the accumulator pressure acting on the piston, so that the ball remains in a suspended state between the two valve positions.